[aprssig] APRS Digipeter Design Questions
oh2kku at iki.fi
Fri Apr 29 11:02:37 CDT 2005
Curt, WE7U wrote:
> Due to Mic-E protocol you also need to include the DEST callsign
> field, as that is part of your location. That means you need
And to be more exact, I guess you'd want to leave the destination SSID
out of the checksum, because it can change when a mic-e packet is
digipeated. OTOH, most digipeaters don't seem to implement destination
SSID digipeating, so it's not that big of a deal in practice.
If one wanted to do a bit fancier duplicate checking, I guess you could
also check the body. If the body contains a third party packet, use the
third party sender/target/body information for duplicate checking. And
also ignore trailing crs, lfs and spaces in packet bodies. I guess a
plain digipeater can ignore these things, but an igate should do these
checks before deciding to gate packets.
Not really relevant to duplicate checking, but checking the digipeater
chain length might be a useful feature as well. I.e. if the packet has
already been digipeated n times, don't digipeat it again (or digipeat,
but truncate the rest of the path).
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